Summary
We propose to adopt a new airworthiness directive (AD) for certain Learjet Inc. Model 45 airplanes. This proposed AD would require replacing aluminum fire extinguisher discharge tubes with new, improved tubes; checking the fire extinguisher container for certain serial numbers; replacing fire extinguisher containers that have affected serial numbers; inspecting the pressure indicator on certain fire extinguisher containers for discrepancies; and performing corrective action if necessary. This proposed AD results from a report of accidental discharge of a fire extinguisher container and damage to an aluminum discharge tube. Investigation revealed that following the discharge an inaccurate pressure indication, due to the indicator dial being incorrectly staked, showed that the container was fully charged. We are proposing this AD to prevent inaccurate pressure readings and subsequent damage to the discharge tubes during operation, which could result in failure of the fire extinguisher system and an uncontained fire in an emergency situation.